arXiv subjects

B. Safonov

Publications and source records attributed to B. Safonov.

14 recordsLinked to original sources

arXiv2026

CAFE follow-up of TESS hot Jupiter candidates left behind: I. Five newly confirmed planets and a false positive

Hot Jupiters are key targets for understanding planet formation, migration, and atmospheres. Yet, most ground-based follow-up resources for the TESS mission are focused on confirming low-mass planet candidates, leaving many giant planets without mass determinations or definitive confirmation. We use the \cafe{} spectrograph at Calar Alto Observatory to monitor the radial velocity of stars hosting hot-Jupiter candidates that have received little follow-up, aiming to confirm their planetary nature. We present results for seven candidates. We monitored the radial velocity of TOI-603, TOI-1137, TOI-1837, TOI-2114, TOI-4492, TOI-5806, and TOI-5811, jointly modeling the CAFE radial velocities and TESS photometry to determine the nature and properties of the transiting objects. We confirm five new planets: TOI-603 b ($33.0^{+6.5}_{-6.2}$ M$_{\oplus}$, $16.2$ d), TOI-2114 b ($1.01^{+0.14}_{-0.12}$ M$_{\rm Jup}$, $6.2$ d), TOI-4492 b ($5.92^{+0.67}_{-0.64}$ M$_{\rm Jup}$, $4.4$ d), TOI-5806 b ($2.77^{+0.34}_{-0.32}$ M$_{\rm Jup}$, $3.2$ d), and TOI-5811 B b ($0.81^{+0.11}_{-0.10}$ M$_{\rm Jup}$, $6.3$ d). TOI-603 b lies in the "Neptune savanna", whereas the other four are hot Jupiters orbiting slightly evolved stars. We find TOI-5811.01 to be a planet transiting the nearby bound companion TOI-5811 B (hence TOI-5811 B b), and identify a stellar companion to TOI-5806 at a projected separation of 248 au, making both S-type planetary systems. TOI-1837.01 is an eclipsing binary, while TOI-1137.01 remains inconclusive. The five confirmed planets orbit bright stars (${\rm G}=8.6-10.2$~mag), and four are excellent targets for atmospheric studies, with transmission spectroscopy metrics above 90. These results highlight the importance of intensive follow-up observations to establish the nature of transiting planet candidates.

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arXiv2024

Characterization of seven transiting systems including four warm Jupiters from SOPHIE and TESS

We present the study of seven systems, three of which TOI-2295, TOI-2537, and TOI-5110 are newly discovered planetary systems. Through the analysis of TESS photometry, SOPHIE radial velocities, and high-spatial resolution imaging, we found that TOI-2295b, TOI-2537b, and TOI-5110b are transiting warm Jupiters with orbital periods ranging from 30 to 94 d, masses between 0.9 and 2.9 MJ, and radii ranging from 1.0 to 1.5 RJ. Both TOI-2295 and TOI-2537 each harbor at least one additional, outer planet. Their outer planets TOI-2295c and TOI-2537c are characterized by orbital periods of 966.5 +/- 4.3 and 1920^{+230}_{-140} d, respectively, and minimum masses of 5.61^{+0.23}_{-0.24} and 7.2 +/- 0.5 MJ, respectively. We also investigated and characterized the two recently reported warm Jupiters TOI-1836b and TOI-5076b, which we independently detected in SOPHIE RVs. Additionally, we study the planetary candidates TOI-4081.01 and TOI-4168.01. For TOI-4081.01, despite our detection in radial velocities, we cannot rule out perturbation by a blended eclipsing binary and thus exercise caution regarding its planetary nature. On the other hand, we identify TOI-4168.01 as a firm false positive. Finally, we highlight interesting characteristics of these new planetary systems. The transits of TOI-2295b are highly grazing, with an impact parameter of 1.056$^{+0.063}_{-0.043}$. TOI-2537b, in turn, is a temperate Jupiter with an effective temperature of 307+/-15 K and can serve as a valuable low-irradiation control for models of hot Jupiter inflation anomalies. We also detected significant transit timing variations (TTVs) for TOI-2537b, which are likely caused by gravitational interactions with the outer planet TOI-2537c. Finally, TOI-5110b stands out due to its orbital eccentricity of 0.75+/- 0.03, one of the highest planetary eccentricities discovered thus far.

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arXiv2024

TOI-1135 b: A young hot Saturn-size planet orbiting a solar-type star

Despite the thousands of planets in orbit around stars known to date, the mechanisms of planetary formation, migration, and atmospheric loss remain unresolved. In this work, we confirm the planetary nature of a young Saturn-size planet transiting a solar-type star every 8.03 d, TOI-1135\,b. The age of the parent star is estimated to be in the interval of 125--1000 Myr based on various activity and age indicators, including its stellar rotation period of 5.13\,$\pm$\,0.27 d and the intensity of photospheric lithium. We obtained follow-up photometry and spectroscopy, including precise radial velocity measurements using the CARMENES spectrograph, which together with the TESS data allowed us to fully characterise the parent star and its planet. As expected for its youth, the star is rather active and shows strong photometric and spectroscopic variability correlating with its rotation period. We modelled the stellar variability using Gaussian process regression. We measured the planetary radius at 9.02\,$\pm$\,0.23 R$_\oplus$ (0.81\,$\pm$\,0.02 R$_{\mathrm{Jup}}$) and determined a 3$σ$ upper limit of $<$\,51.4 M$_\oplus$ ($<$\,0.16 \,M$_{\rm{Jup}}$) on the planetary mass by adopting a circular orbit. Our results indicate that TOI-1135\,b is an inflated planet less massive than Saturn or Jupiter but with a similar radius, which could be in the process of losing its atmosphere by photoevaporation. This new young planet occupies a region of the mass-radius diagram where older planets are scarse, and it could be very helpful to understanding the lower frequency of planets with sizes between Neptune and Saturn.

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arXiv2022

Orbital parameters and activity of ZZ Tau -- a low mass young binary with circumbinary disc

We present the results of our new observations of the young binary ZZ Tau with a circumbinary disc. The system was found to consist of two coeval (age $<2$ Myr) classical T Tauri stars with the total mass $0.86 \pm 0.09$ M$_\odot$, orbital period $46.8 \pm 0.8$ yr, semimajor axis $88.2 \pm 2.1$ mas, eccentricity $0.58 \pm 0.02$ and the orbital inclination $123.^{\rm o} 8 \pm 1.^{\rm o} 0.$ The accretion rate of ZZ Tau A and ZZ Tau B are approximately $7\times 10^{-10}$ and $2\times 10^{-10}$ M$_\odot$ yr$^{-1},$ respectively. No correlation was found between the long-term photometric variability of ZZ Tau and orbital position of its components. The periodic light variations with $P=4.171 \pm 0.002$ days was observed in the $BVRI$ bands presumably connected with an accretion (hot) spot on the surface of the primary (ZZ Tau A). At the same time no periodicity was observed in the $U$ band nor in the emission line profile variations probably due to the significant contribution of ZZ Tau B's emission, which dominates shortward of $λ\approx 0.4\,μ$m. We argue that the extinction in the direction to the primary is noticeably larger than that to the secondary. It appeared that the rotation axis of the primary is inclined to the line of sight by $\approx 31^{\rm o} \pm 4^{\rm o}.$ We concluded also that ZZ Tau is the source of an CO molecular outflow, however, ZZ Tau IRS rather than ZZ Tau is the source of the Herbig-Haro object HH393.

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arXiv2021

TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf

Thanks to the relative ease of finding and characterizing small planets around M dwarf stars, these objects have become cornerstones in the field of exoplanet studies. The current paucity of planets in long-period orbits around M dwarfs make such objects particularly compelling as they provide clues about the formation and evolution of these systems. In this study, we present the discovery of TOI-2257 b (TIC 198485881), a long-period (35 d) sub-Neptune orbiting an M3 star at 57.8pc. Its transit depth is about 0.4%, large enough to be detected with medium-size, ground-based telescopes. The long transit duration suggests the planet is in a highly eccentric orbit ($e \sim 0.5$), which would make it the most eccentric planet that is known to be transiting an M-dwarf star. We combined TESS and ground-based data obtained with the 1.0-m SAINT-EX, 0.60-m TRAPPIST-North and 1.2-m FLWO telescopes to find a planetary size of 2.2 $R_{\oplus}$ and an orbital period of 35.19 days. In addition, we make use of archival data, high-resolution imaging, and vetting packages to support our planetary interpretation. With its long period and high eccentricity, TOI-2257 b falls in a novel slice of parameter space. Despite the planet's low equilibrium temperature ($\sim$ 256 K), its host star's small size ($R_* = 0.311 \pm{0.015}$) and relative infrared brightness (K$_{mag}$ = 10.7) make it a suitable candidate for atmospheric exploration via transmission spectroscopy.

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arXiv2020

RW Aur B: a modest UX Ori type companion of the famous primary

The secondary of the famous young binary RW Aur is much less studied than the primary. To compensate this shortcoming, we present here the results of UBVRIJHK photometric, VRI polarimetric and optical spectral observations of RW Aur B. The star demonstrates chaotic brightness variations in the optical band with irregular short (~ 1 day) dimmings with an amplitude $ΔV$ up to $1.3^{\rm m}.$ The dimmings are accompanied with an increase in the linear polarization (up to 3 per cent in the I band), presumably due to the scattering of the stellar radiation by dust in the circumstellar disc that means that RW Aur B can be classified as a UX Ori type star. We concluded that the observed excess emission at $λ\lesssim 0.45$ $μ$m and longward $\approx$ 2 $μ$m as well as a variability of fluxes and profiles of HI, HeI and NaI D emission lines are due to the accretion process. At the same time, emission components of Ca II lines indicate that RW Aur B has a powerful chromosphere. Assuming the solar elemental abundances, we found the following parameters of the star: $T_{\rm eff} = 4100-4200$ K, $A_{\rm V}=0.6 \pm 0.1$ (out of the dimming events), $L_* \approx 0.6$ $L_\odot,$ $R_* \approx 1.5$ $R_\odot,$ $M\approx 0.85$ M$_\odot,$ $\dot M_{\rm acc}<5\times 10^{-9}$ M$_\odot$ yr$^{-1}.$ Finally, we discuss possible reasons for the different levels of the accretion activity of RW Aur binary components and present arguments in favour of the fact that they are gravitationally bound.

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arXiv2018

Analysis of colour and polarimetric variability of RW Aur A in 2010-2018

Results of $UBVRIJHKLM$ photometry and $VRI$ polarimetry of a young star RW Aur A observed during unprecedented long and deep (up to $ΔV \approx 5$ mag) dimming events in 2010-11 and 2014-18 are presented. The polarization degree $p$ of RW Aur A at this period has reached 30 per cent in the $I$ band. As in the case of UX Ori type stars (UXORs), the so-called 'bluing effect' in the colour-magnitude $V$ versus $V-R_{\rm c},$ $V-I_{\rm c}$ diagrams of the star and a strong anticorrelation between $p$ and brightness were observed. But the duration and the amplitude of the eclipses as well as the value and orientation of polarization vector in our case differ significantly from that of UXORs. We concluded that the dimmings of RW Aur A occurred due to eclipses of the star and inner regions of its disc by the axisymmetric dust structure located above the disc and created by the disc wind. Taking into account both scattering and absorption of stellar light by the circumstellar dust, we explain some features of the light curve and the polarization degree - magnitude dependence. We found that near the period of minimal brightness mass-loss rate of the dusty wind was $> 10^{-9}$ M$_\odot$ yr$^{-1}.$

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arXiv2017

Anomalous eclipses of the young star RW Aur A

Results of UBVRIJHKLM photometry, VRI polarimetry and optical spectroscopy of a young star RW Aur A obtained during 2010-11 and 2014-16 dimming events are presented. During the second dimming the star decreased its brightness to ΔV > 4.5 mag, polarization of its light in I-band was up to 30%, and color-magnitude diagram was similar to that of UX Ori type stars. We conclude that the reason of both dimmings is an eclipses of the star by dust screen, but the size of the screen is much larger than in the case of UXORs.

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arXiv2016

Night-sky brightness and extinction at Mt. Shatdzhatmaz

The photometric sky quality of Mt. Shatdzhatmaz, the site of Sternberg Astronomical Institute Caucasian Observatory 2.5 m telescope, is characterized here by the statistics of the night-time sky brightness and extinction. The data were obtained as a by-product of atmospheric optical turbulence measurements with the MASS (Multi-Aperture Scintillation Sensor) device conducted in 2007--2013. The factors biasing night-sky brightness measurements are considered and a technique to reduce their impact on the statistics is proposed. The single-band photometric estimations provided by MASS are easy to transform to the standard photometric bands. The median moonless night-sky brightness is 22.1, 21.1, 20.3, and 19.0 mag per square arcsec for the $B$, $V$, $R$, and $I$ spectral bands, respectively. The median extinction coefficients for the same photometric bands are 0.28, 0.17, 0.13, and 0.09 mag. The best atmospheric transparency is observed in winter.

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arXiv2014

Resolved photometry of the binary components of RW Aur

Resolved UBVRI photometry of RW Aur binary was performed on November 13/14, 2014 during the deep dimming of RW Aur with a newly installed 2.5 meter telescope of the Caucasus observatory of Lomonosov Moscow State University at the mount Shatzhatmaz. At that moment RW Aur A was $\simeq 3^m$ fainter than in November 1994 in all spectral bands. We explain the current RW Aur A dimming as a result of eclipse of the star by dust particles with size $>1 μm.$ We found that RW Aur B is also a variable star: it was brighter than 20 years ago at $0.7^m$ in each of UBVRI band (gray brightening).

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arXiv2011

Differential image motion in the short exposure regime

Whole atmosphere seeing β_0 is the most important parameter in site testing measurements. Estimation of the seeing from a variance of differential image motion is always biased by a non-zero DIMM exposure, which results in a wind smoothing. In the paper, the wind effects are studied within short exposure approximation, i.e. when the wind shifts turbulence during exposure by distance lesser than device aperture. The method of correction for this effect on the base of image motion correlation between adjacent frames is proposed. It is shown that the correlation can be used for estimation of the mean wind speed V_2 and atmospheric coherence time τ_0. Total power of longitudinal and transverse image motion is suggested for elimination of dependence on the wind direction. Obtained theoretical results were tested on the data obtained on Mount Shatdjatmaz in 2007--2010 with MASS/DIMM device and good agreement was found.

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arXiv2010

First results of site testing program at Mt. Shatdzhatmaz in 2007 - 2009

We present the first results of the site testing performed at Mt.~Shatdzhatmaz at Northern Caucasus, where the new Sternberg astronomical institute 2.5-m telescope will be installed. An automatic site monitor instrumentation and functionality are described together with the methods of measurement of the basic astroclimate and weather parameters. The clear night sky time derived on the basis of 2006 -- 2009 data amounts to 1340 hours per year. Principle attention is given to the measurement of the optical turbulence altitude distribution which is the most important characteristic affecting optical telescopes performance. For the period from November 2007 to October 2009 more than 85\,000 turbulence profiles were collected using the combined MASS/DIMM instrument. The statistical properties of turbulent atmosphere above the summit are derived and the median values for seeing $β_0 = 0.93$~arcsec and free-atmosphere seeing $β_{free} = 0.51$~arcsec are determined. Together with the estimations of isoplanatic angle $θ_0 = 2.07$~arcsec and time constant $τ_0 = 2.58 \mbox{ ms}$, these are the first representative results obtained for Russian sites which are necessary for development of modern astronomical observation techniques like adaptive optics.

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arXiv2009

Measurement of optical turbulence in free atmosphere above Mt.Maidanak in 2005-2007

Results of 2005-2007 campaign of measurement of the optical turbulence vertical distribution above Mt. Maidanak are presented. Measurements are performed with the MASS (Multi-Aperture Scintillation Sensor) device which is widely used in similar studies during last years at several observatories across the world. The data analysis shows that median seeing in free atmosphere (at altitudes above 0.5km) is 0.46 arcsec and median isoplanatic angle is 2.47 arcsec. Given a rather long atmospheric coherence time (about 7 ms when the seeing is good) such conditions are favorable for adaptive optics and interferometry in the visible and near-IR.

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arXiv2007

Combined MASS-DIMM instrument for atmospheric turbulence studies

Several site-testing programs and observatories currently use combined MASS-DIMM instruments for monitoring parameters of optical turbulence. The instrument is described here. After a short recall of the measured quantities and operational principles, the optics and electronics of MASS-DIMM, interfacing to telescopes and detectors, and operation are covered in some detail. Particular attention is given to the correct measurement and control of instrumental parameters to ensure valid and well-calibrated data, to the data quality and filtering. Examples of MASS-DIMM data are given, followed by the list of present and future applications.

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