arXiv subjects

R. Szakats

Publications and source records attributed to R. Szakats.

13 recordsLinked to original sources

arXiv2025

A high geometric albedo and small size of the Haumea cluster member (24835) 1995 SM55 from a stellar occultation and photometric observations

Trans-Neptunian objects (TNOs) are among the most ancient bodies of the solar system. Understanding their physical properties is key to constraining their origin and the evolution of the outer regions beyond Neptune. Stellar occultations provide highly accurate size and shape information. (24835) 1995 SM55 is one of the few members of the Haumea cluster and thus of particular interest. We aimed to determine its projected size, absolute magnitude, and geometric albedo, and to compare these with Haumea. A stellar occultation on 25 February 2024 was observed from five sites, with seven positive detections and 33 negative chords. An elliptical fit to the occultation chords yields semi-axes of $(104.3 \pm 0.4) \times (83.5 \pm 0.5)$ km, giving an area-equivalent diameter of $186.7 \pm 1.8$ km, smaller than the 250 km upper limit from Herschel thermal data. Photometry provides an absolute magnitude $H_V = 4.55 \pm 0.03$, a phase slope of $0.04 \pm 0.02$ mag/deg, and a $V-R = 0.37 \pm 0.05$. The rotational variability has an amplitude $Δm = 0.05$ mag, but the period remains uncertain. Combining occultation and photometry, we derive a geometric albedo $p_V = 0.80 \pm 0.04$, one of the highest values measured for a TNO. This value is slightly higher than that of Haumea, consistent with the interpretation that 1995 SM55 belongs to the Haumea cluster.

astro-ph.EP↗

arXiv2025

SN 2023ixf in M101: physical parameters from bolometric light curve modeling

We present new photometric observations of the core-collapse supernova SN 2023ixf occurred in M101, taken with the RC80 and BRC80 robotic telescopes in Hungary. The initial nickel mass from the late-phase bolometric light curve extending up to 400 days after explosion, is inferred as $M_{\rm Ni} = 0.046 \pm 0.007$ M$_\odot$. The comparison of the bolometric light curve with models from hydrodynamical simulations as well as semi-analytic radiative diffusion codes reveals a relatively low-mass ejecta of $M_{\rm ej} \lesssim 9$ M$_\odot$, contrary to SN~2017eaw, another H-rich core-collapse event, which had $M_{\rm ej} \gtrsim 15$ M$_\odot$.

astro-ph.HE↗

arXiv2025

Asteroid sizes determined with thermophysical model and stellar occultations

Context. The sizes of many asteroids, especially slowly rotating, low-amplitude targets, remain poorly constrained due to selection effects. These biases limit the availability of high-quality data, leaving size estimates reliant on spherical shape assumptions. Such approximations introduce significant uncertainties propagating, e.g. into density determinations or thermophysical and compositional studies, affecting our understanding of asteroid properties. Aims. This work targets poorly studied main-belt asteroids, most of which lacked shape models. Using only high-quality dense light curves, thermal IR observations (incl. WISE), and stellar occultations, we aimed to produce reliable shape models and scale them via two independent techniques, allowing size comparison. We conducted two campaigns to obtain dense photometric light curves and to acquire multi-chord stellar occultations. Methods. Shape and spin models were reconstructed using lightcurve inversion. Sizes were determined by (1) thermophysical modeling with the Convex Inversion Thermophysical Model (CITPM), optimizing spin and shape models to visible lightcurve and IR data, and (2) scaling shape models with stellar occultations. Results. We obtained precise sizes and shape models for 15 asteroids. CITPM- and occultation-derived sizes agree within 5% in most cases, demonstrating the modeling's reliability. Larger discrepancies usually stem from incomplete occultation chord coverage. The study also gives insights into surface properties incl. albedo, roughness and thermal inertia. Conclusions. Using high-quality data and an advanced TPM integrating thermal and visible data with shape adjustment enabled precise size estimates comparable to those from multi-chord stellar occultations. We resolved major inconsistencies in previous size estimates, providing solid input for future studies on asteroid densities and surfaces.

astro-ph.EP↗

arXiv2022

Physical properties of the trans-Neptunian object (38628) Huya from a multi-chord stellar occultation

Within our international program to obtain accurate physical properties of trans-Neptunian objects (TNOs) we predicted a stellar occultation by the TNO (38628) Huya of the star Gaia DR2 4352760586390566400 (mG = 11.5 mag.) for March 18, 2019. After an extensive observational campaign, we updated the prediction and it turned out to be favorable to central Europe. Therefore, we mobilized half a hundred professional and amateur astronomers, and the occultation was finally detected from 21 telescopes located at 18 sites. This makes the Huya event one of the best ever observed stellar occultation by a TNO in terms of the number of chords. We determine accurate size, shape, and geometric albedo, and we also provide constraints on the density and other internal properties of this TNO. The 21 positive detections of the occultation by Huya allowed us to obtain well-separated chords which permitted us to fit an ellipse for the limb of the body at the moment of the occultation (i.e., the instantaneous limb) with kilometric accuracy. The projected semi-major and minor axes of the best ellipse fit obtained using the occultation data are (a', b') = (217.6 $\pm$ 3.5 km, 194.1 $\pm$ 6.1 km) with a position angle of the minor axis P' = 55.2 $\pm$ 9.1 degrees. From this fit, the projected area-equivalent diameter is 411.0 $\pm$ 7.3 km. This diameter is compatible with the equivalent diameter for Huya obtained from radiometric techniques (D = 406 $\pm$ 16 km). From this instantaneous limb, we obtained the geometric albedo for Huya (p$\rm_V$ = 0.079 $\pm$ 0.004) and we explored possible 3D shapes and constraints to the mass density for this TNO. We did not detect the satellite of Huya through this occultation, but the presence of rings or debris around Huya is constrained using the occultation data. We also derived an upper limit for a putative Pluto-like global atmosphere of about p$_{\rm surf}$ = 10 nbar.

astro-ph.EP↗

arXiv2022

The multichord stellar occultation on 2019 October 22 by the trans-Neptunian object (84922) 2003 VS$_2$

We predicted, observed, and analyzed the multichord stellar occultation of the Second Gaia Data Release (Gaia DR2) source 3449076721168026624 (m$_v$ = 14.1 mag) by the plutino object 2003 VS$_2$ (hereafter, VS$_2$) on 2019 October 22. We also carried out photometric observations to derive the rotational light curve amplitude and rotational phase of VS$_2$ during the stellar occultation. Combining the results and assuming a triaxial shape, we derived the 3D shape of VS$_2$. Out of the 39 observatories involved in the observational campaign, 12 sites reported a positive detection; this makes it one of the best observed stellar occultations by a TNO so far. We obtained a rotational light curve amplitude of $Δ$m = 0.264 $\pm$ 0.017 mag, a mean area-equivalent diameter of D$_{A_{eq}}$ = 545 $\pm$ 13 km, and a geometric albedo of 0.134 $\pm$ 0.010. The best triaxial shape obtained for VS$_2$ has semiaxes a = 339 $\pm$ 5 km, b = 235 $\pm$ 6 km, and c = 226 $\pm$ 8 km. The derived aspect angle is $θ$ = 59$° \pm$ 2$°$ or its supplementary $θ$ = 121$° \pm$ 2$°$, depending on the north-pole position. The spherical-volume equivalent diameter is D$_{V_{eq}}$ = 524 $\pm$ 7 km. If we consider large albedo patches on its surface, the semi-major axis of the ellipsoid could be ~10 km smaller. These results are compatible with the previous ones determined from the single-chord 2013 and four-chord 2014 stellar occultations and with the effective diameter and albedo derived from Herschel and Spitzer data. They provide evidence that VS$_2$'s 3D shape is not compatible with a homogeneous triaxial body in hydrostatic equilibrium, but it might be a differentiated body and/or might be sustaining some stress. No secondary features related to rings or material orbiting around VS$_2$ were detected.

astro-ph.EP↗

arXiv2020

SN 2018zd: An Unusual Stellar Explosion as Part of the Diverse Type II Supernova Landscape

We present extensive observations of SN 2018zd covering the first $\sim450$\,d after the explosion. This SN shows a possible shock-breakout signal $\sim3.6$\,hr after the explosion in the unfiltered light curve, and prominent flash-ionisation spectral features within the first week. The unusual photospheric temperature rise (rapidly from $\sim 12,000$\,K to above 18,000\,K) within the earliest few days suggests that the ejecta were continuously heated. Both the significant temperature rise and the flash spectral features can be explained with the interaction of the SN ejecta with the massive stellar wind ($0.18^{+0.05}_{-0.10}\, \rm M_{\odot}$), which accounts for the luminous peak ($L_{\rm max} = [1.36\pm 0.63] \times 10^{43}\, \rm erg\,s^{-1}$) of SN 2018zd. The luminous peak and low expansion velocity ($v \approx 3300$ km s$^{-1}$) make SN 2018zd to be like a member of the LLEV (luminous SNe II with low expansion velocities) events originated due to circumstellar interaction. The relatively fast post-peak decline allows a classification of SN 2018zd as a transition event morphologically linking SNe~IIP and SNe~IIL. In the radioactive-decay phase, SN 2018zd experienced a significant flux drop and behaved more like a low-luminosity SN~IIP both spectroscopically and photometrically. This contrast indicates that circumstellar interaction plays a vital role in modifying the observed light curves of SNe~II. Comparing nebular-phase spectra with model predictions suggests that SN 2018zd arose from a star of $\sim 12\,\rm M_{\odot}$. Given the relatively small amount of $^{56}$Ni ($0.013 - 0.035 \rm M_{\odot}$), the massive stellar wind, and the faint X-ray radiation, the progenitor of SN 2018zd could be a massive asymptotic giant branch star which collapsed owing to electron capture.

astro-ph.HE↗

arXiv2020

Constraints on the physical properties of Type Ia supernovae from photometry

We present a photometric study of 17 Type Ia supernovae (SNe) based on multi-color (Bessell BVRI) data taken at Piszkesteto mountain station of Konkoly Observatory, Hungary between 2016 and 2018. We analyze the light curves (LCs) using the publicly available LC-fitter SNooPy2 to derive distance and reddening information. The bolometric LCs are fit with a radiation-diffusion Arnett-model to get constraints on the physical parameters of the ejecta: the optical opacity, the ejected mass and the expansion velocity in particular. We also study the pre-maximum (B-V) color evolution by comparing our data with standard delayed detonation and pulsational delayed detonation models, and show that the Ni56 masses of the models that fit the (B-V) colors are consistent with those derived from the bolometric LC fitting. We find similar correlations between the ejecta parameters (e.g. ejecta mass, or Ni56 mass vs decline rate) as published recently by Scalzo et al. (2019).

astro-ph.HE↗

arXiv2019

(704) Interamnia: A transitional object between a dwarf planet and a typical irregular-shaped minor body

With an estimated diameter in the 320 to 350 km range, (704) Interamnia is the fifth largest main belt asteroid and one of the few bodies that fills the gap in size between the four largest bodies with $D$ > 400 km (Ceres, Vesta, Pallas and Hygiea) and the numerous smaller bodies with $D$ $\lesssim$ 200 km. However, despite its large size, little is known about the shape and spin state of Interamnia and, therefore, about its bulk composition and past collisional evolution. We aimed to test at what size and mass the shape of a small body departs from a nearly ellipsoidal equilibrium shape (as observed in the case of the four largest asteroids) to an irregular shape as routinely observed in the case of smaller ($D$ $\lesssim$ 200 km) bodies. We observed Interamnia as part of our ESO VLT/SPHERE large program (ID: 199.C-0074) at thirteen different epochs. In addition, several new optical lightcurves were recorded. These data, along with stellar occultation data from the literature, were fed to the All-Data Asteroid Modeling (ADAM) algorithm to reconstruct the 3D-shape model of Interamnia and to determine its spin state. Interamnia's volume-equivalent diameter of 332 $\pm$ 6 km implies a bulk density of $ρ$=1.98 $\pm$ 0.68 gcm$^{-3}$ , which suggests that Interamnia - like Ceres and Hygiea - contains a high fraction of water ice, consistent with the paucity of apparent craters. Our observations reveal a shape that can be well approximated by an ellipsoid, and that is compatible with a fluid hydrostatic equilibrium at the 2 $σ$ level. The rather regular shape of Interamnia implies that the size and mass limit, under which the shapes of minor bodies with a high amount of water ice in the subsurface become irregular, has to be searched among smaller ($D$ $\lesssim$ 300km) less massive ($m$ $\lesssim$ 3x10$^{19}$ kg) bodies.

astro-ph.EP↗

arXiv2018

SN 2016coi/ASASSN-16fp: An example of residual helium in a type Ic supernova?

The optical observations of Ic-4 supernova (SN) 2016coi/ASASSN-16fp, from $\sim 2$ to $\sim450$ days after explosion, are presented along with analysis of its physical properties. The SN shows the broad lines associated with SNe Ic-3/4 but with a key difference. The early spectra display a strong absorption feature at $\sim 5400$ Å which is not seen in other SNe~Ic-3/4 at this epoch. This feature has been attributed to He I in the literature. Spectral modelling of the SN in the early photospheric phase suggests the presence of residual He in a C/O dominated shell. However, the behaviour of the He I lines are unusual when compared with He-rich SNe, showing relatively low velocities and weakening rather than strengthening over time. The SN is found to rise to peak $\sim 16$ d after core-collapse reaching a bolometric luminosity of Lp $\sim 3\times10^{42}$ \ergs. Spectral models, including the nebular epoch, show that the SN ejected $2.5-4$ \msun\ of material, with $\sim 1.5$ \msun\ below 5000 \kms, and with a kinetic energy of $(4.5-7)\times10^{51}$ erg. The explosion synthesised $\sim 0.14$ \msun\ of 56Ni. There are significant uncertainties in E(B-V)host and the distance however, which will affect Lp and MNi. SN 2016coi exploded in a host similar to the Large Magellanic Cloud (LMC) and away from star-forming regions. The properties of the SN and the host-galaxy suggest that the progenitor had $M_\mathrm{ZAMS}$ of $23-28$ \msun\ and was stripped almost entirely down to its C/O core at explosion.

astro-ph.HE↗

arXiv2016

Activity of 50 Long-Period Comets Beyond 5.2 AU

Remote investigations of the ancient solar system matter has been traditionally carried out through the observations of long-period (LP) comets that are less affected by solar irradiation than the short-period counterparts orbiting much closer to the Sun. Here we summarize the results of our decade-long survey of the distant activity of LP comets. We found that the most important separation in the dataset is based on the dynamical nature of the objects. Dynamically new comets are characterized by a higher level of activity on average: the most active new comets in our sample can be characterized by afrho values >3--4 higher than that of our most active returning comets. New comets develop more symmetric comae, suggesting a generally isotropic outflow. Contrary to this, the coma of recurrent comets can be less symmetrical, ocassionally exhibiting negative slope parameters, suggesting sudden variations in matter production. The morphological appearance of the observed comets is rather diverse. A surprisingly large fraction of the comets have long, teniouos tails, but the presence of impressive tails does not show a clear correlation with the brightness of the comets.

astro-ph.EP↗

arXiv2016

Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej

We present extensive optical ($UBVRI$, $g'r'i'z'$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9\pm0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2\% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $\lambda6355$ as early as +8 days. The photospheric velocity ($v_{\rm ph}$) is determined by modeling the spectra in the vicinity of Fe II $\lambda5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{\rm ph} = 4500\pm500$ km s$^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94\pm7$ days long, yields an explosion energy of $0.9\pm0.3\times10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2\pm4.2$~M$_\odot$ and a radius of $250\pm70$~R$_\odot$. We observe a broken exponential profile beyond +120 days, with a break point at +$183\pm16$ days. Measurements beyond this break time yield a $^{56}$Ni mass of $0.013\pm0.001$~M$_\odot$.

astro-ph.SR↗

arXiv2012

Testing SNe Ia distance measurement methods with SN 2011fe

The nearby, bright, almost completely unreddened Type Ia supernova 2011fe in M101 provides a unique opportunity to test both the precision and the accuracy of the extragalactic distances derived from SNe Ia light curve fitters. We apply the current, public versions of the independent light curve fitting codes MLCS2k2 and SALT2 to compute the distance modulus of SN 2011fe from high-precision, multi-color (BVRI) light curves. The results from the two fitting codes confirm that 2011fe is a "normal" (not peculiar) and only slightly reddened SN Ia. New unreddened distance moduli are derived as 29.21 +/- 0.07 mag (D ~ 6.95 +/- 0.23$ Mpc, MLCS2k2), and 29.05 +/- 0.07 mag (6.46 +/- 0.21 Mpc, SALT2). Despite the very good fitting quality achieved with both light curve fitters, the resulting distance moduli are inconsistent by 2 sigma. Both are marginally consistent (at ~1 sigma) with the HST Key Project distance modulus for M101. The SALT2 distance is in good agreement with the recently revised Cepheid- and TRGB-distance to M101. Averaging all SN- and Cepheid-based estimates, the absolute distance to M101 is ~6.6 +/- 0.5 Mpc.

astro-ph.CO↗

arXiv2008

Binarity and multiperiodicity in high-amplitude delta Scuti stars

We have carried out a photometric and spectroscopic survey of bright high-amplitude delta Scuti (HADS) stars. The aim was to detect binarity and multiperiodicity (or both) in order to explore the possibility of combining binary star astrophysics with stellar oscillations. Here we present the first results for ten, predominantly southern, HADS variables. We detected the orbital motion of RS Gru with a semi-amplitude of ~6.5 km/s and 11.5 days period. The companion is inferred to be a low-mass dwarf star in a close orbit around RS Gru. We found multiperiodicity in RY Lep both from photometric and radial velocity data and detected orbital motion in the radial velocities with hints of a possible period of 500--700 days. The data also revealed that the amplitude of the secondary frequency is variable on the time-scale of a few years, whereas the dominant mode is stable. Radial velocities of AD CMi revealed cycle-to-cycle variations which might be due to non-radial pulsations. We confirmed the multiperiodic nature of BQ Ind, while we obtained the first radial velocity curves of ZZ Mic and BE Lyn. The radial velocity curve and the O-C diagram of CY Aqr are consistent with the long-period binary hypothesis. We took new time series photometry on XX Cyg, DY Her and DY Peg, with which we updated their O-C diagrams.

astro-ph↗