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1. Constraints on the evolution of the Triton atmosphere from occultations: 1989–2022.

Author

Sicardy, B., Tej, A., Gomes-Júnior, A. R., Romanov, F. D., Bertrand, T., Ashok, N. M., Lellouch, E., Morgado, B. E., Assafin, M., Desmars, J., Camargo, J. I. B., Kilic, Y., Ortiz, J. L., Vieira-Martins, R., Braga-Ribas, F., Ninan, J. P., Bhatt, B. C., Pramod Kumar, S., Swain, V., and Sharma, S.

Subjects
ATMOSPHERIC pressure measurement, SURFACE pressure, VAPOR pressure, ATMOSPHERE, ATMOSPHERIC pressure
Abstract

Context. In about 2000, the south pole of Triton experienced an extreme summer solstice that occurs every ∼650 years, when the subsolar latitude reached about 50°S. Bracketing this epoch, a few occultations probed the Triton atmosphere in 1989, 1995, 1997, 2008, and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of the atmospheric pressure on Triton. This is presented here. Aims. The goal is to constrain the volatile transport models (VTMs) of the Triton atmosphere. The atmosphere is basically in vapor pressure equilibrium with the nitrogen ice at its surface. Methods. Fits to the occultation light curves yield the atmospheric pressure of Triton at the reference radius 1400 km, from which the surface pressure is deduced. Results. The fits provide a pressure p1400 = 1.211 ± 0.039 μbar at radius 1400 km (47 km altitude), from which a surface pressure of psurf = 14.54 ± 0.47 μbar is deduced (1σ error bars). To within the error bars, this is identical to the pressure derived from the previous occultation of 5 October 2017, p1400 = 1.18 ± 0.03 μbar and psurf = 14.1 ± 0.4 μbar, respectively. Based on recent models of the volatile cycles of Triton, the overall evolution of the surface pressure over the last 30 years is consistent with N2 condensation taking place in the northern hemisphere. However, models typically predict a steady decrease in the surface pressure for the period 2005-2060, which is not confirmed by this observation. Complex surface-atmosphere interactions, such as ice albedo runaway and formation of local N2 frosts in the equatorial regions of Triton, could explain the relatively constant pressure between 2017 and 2022. [ABSTRACT FROM AUTHOR]

Published
2024
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2. GRANDMA and HXMT Observations of GRB 221009A -- the Standard-Luminosity Afterglow of a Hyper-Luminous Gamma-Ray Burst

Author

Kann, D. A., Agayeva, S., Aivazyan, V., Alishov, S., Andrade, C. M., Antier, S., Baransky, A., Bendjoya, P., Benkhaldoun, Z., Beradze, S., Berezin, D., Boër, M., Broens, E., Brunier, S., Bulla, M., Burkhonov, O., Burns, E., Chen, Y., Chen, Y. P., Conti, M., Coughlin, M. W., Cui, W. W., Daigne, F., Delaveau, B., Devillepoix, H. A. R., Dietrich, T., Dornic, D., Dubois, F., Ducoin, J. -G., Durand, E., Duverne, P. -A., Eggenstein, H. -B., Ehgamberdiev, S., Fouad, A., Freeberg, M., Froebrich, D., Ge, M. Y., Gervasoni, S., Godunova, V., Gokuldass, P., Gurbanov, E., Han, D. W., Hasanov, E., Hello, P., Hussenot-Desenonges, T., Inasaridze, R., Iskandar, A., Ismailov, N., Janati, A., Laz, T. Jegou du, Jia, S. M., Karpov, S., Kaeouach, A., Kiendrebeogo, R. W., Klotz, A., Kneip, R., Kochiashvili, N., Kunert, N., Lekic, A., Leonini, S., Li, C. K., Li, W., Li, X. B., Liao, J. Y., Logie, L., Lu, F. J., Mao, J., Marchais, D., Ménard, R., Morris, D., Natsvlishvili, R., Nedora, V., Noonan, K., Noysena, K., Orange, N. B., Pang, P. T. H., Peng, H. W., Pellouin, C., Peloton, J., Pradier, T., Pyshna, O., Rajabo, Y., Rau, S., Rinner, C., Rivet, J. -P., Romanov, F. D., Rosi, P., Rupchandani, V. A., Serrau, M., Shokry, A., Simon, A., Smith, K., Sokoliuk, O., Soliman, M., Song, L. M., Takey, A., Tillayev, Y., Ramirez, L. M. Tinjaca, Melo, I. Tosta e, Turpin, D., Postigo, A. de Ugarte, Vanaverbeke, S., Vasylenko, V., Vernet, D., Vidadi, Z., Wang, C., Wang, J., Wang, L. T., Wang, X. F., Xiong, Shaolin L., Xu, Y. P., Xue, W. C., Zeng, X., Zhang, S. N., Zhao, H. S., Zhao, X. F., Astrophysique Relativiste Théories Expériences Métrologie Instrumentation Signaux (ARTEMIS), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Joseph Louis LAGRANGE (LAGRANGE), Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut Polytechnique des Sciences Avancées (IPSA), Centre de Physique des Particules de Marseille (CPPM), Aix Marseille Université (AMU)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratoire de Physique des 2 Infinis Irène Joliot-Curie (IJCLab), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT), Institut de recherche en astrophysique et planétologie (IRAP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Observatoire de la Côte d'Azur (OCA), and Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Optical telescopes, Individual: GRB 221009A, Interstellar dust extinction, FOS: Physical sciences, Gamma-ray bursts, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Optical astronomy
Abstract

GRB 221009A is the brightest Gamma-Ray Burst (GRB) detected in more than 50 years of study. In this paper, we present observations in the X-ray and optical domains after the GRB obtained by the GRANDMA Collaboration (which includes observations from more than 30 professional and amateur telescopes) and the Insight-HXMT Collaboration. We study the optical afterglow with empirical fitting from GRANDMA+HXMT data, augmented with data from the literature up to 60 days. We then model numerically, using a Bayesian approach, the GRANDMA and HXMT-LE afterglow observations, that we augment with Swift-XRT and additional optical/NIR observations reported in the literature. We find that the GRB afterglow, extinguished by a large dust column, is most likely behind a combination of a large Milky-Way dust column combined with moderate low-metallicity dust in the host galaxy. Using the GRANDMA+HXMT-LE+XRT dataset, we find that the simplest model, where the observed afterglow is produced by synchrotron radiation at the forward external shock during the deceleration of a top-hat relativistic jet by a uniform medium, fits the multi-wavelength observations only moderately well, with a tension between the observed temporal and spectral evolution. This tension is confirmed when using the extended dataset. We find that the consideration of a jet structure (Gaussian or power-law), the inclusion of synchrotron self-Compton emission, or the presence of an underlying supernova do not improve the predictions, showing that the modelling of GRB22109A will require going beyond the most standard GRB afterglow model. Placed in the global context of GRB optical afterglows, we find the afterglow of GRB 221009A is luminous but not extraordinarily so, highlighting that some aspects of this GRB do not deviate from the global known sample despite its extreme energetics and the peculiar afterglow evolution., Accepted to ApJL for the special issue, 37 pages, 23 pages main text, 6 tables, 13 figures

Published
2023

3. The Fast Evolving, Tremendous and Blue Superoutburst in ASASSN-21au Reveals a Dichotomy in the Outbursts of Long Period AM CVns

Author

Rivera Sandoval, L.E., Heinke, C.O., Hameury, J.M., Cavecchi, Y., Vanmunster, T., Tordai, T., Romanov, F., Observatoire astronomique de Strasbourg (ObAS), and Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

We report on the discovery of a dichotomy in the behavior of outbursts in ultracompact accreting white dwarf binaries (AM CVns), using multiwavelength observations of the new AM CVn system ASASSN-21au which has a period of ~58 min. The binary showed a first brightness increase with respect to its quiescent g level of ~0.8 mag which lasted for at least 82 days, followed by an additional 0.5 mag increase which lasted 2 weeks. Afterwards ASASSN-21au went into superoutburst for the first time. Such superoutburst lasted a total of 19 days, showing an amplitude with respect to quiescence of ~7.5 mags in g, with a precursor and an echo outburst. During the superoutburst of ASASSN-21au we also detected the first correlation between the X-rays, UV and optical emission in an AM CVn. The color evolution of ASASSN-21au indicates that during the superoutburst the dominant component was the accretion disk. The short duration, large amplitude and color evolution of the superoutburst agree with expectations from the disk instability model, but they contrast with the long duration (longer than a year), small amplitude and red color evolution of the outbursts of SDSS~J080710+485259 and SDSS J113732+405458, which have periods of ~53 min and ~60 min, respectively. The initial slow brightness increase in the light curve of ASASSN-21au and the behavior after the superoutburst favors a scenario in which changes in the mass-transfer rate led to disk instabilities, while the outburst mechanism of SDSS J080710+485259 and SDSS J113732+405458 has been attributed to enhanced mass-transfer alone. Further observations are needed to understand the origin of this dichotomy.

Published
2021

4. The Fast Evolving, Tremendous Blue Superoutburst in ASASSN-21au Reveals a Dichotomy in the Outbursts of Long-period AM CVns.

Author

Rivera Sandoval, L. E., Heinke, C. O., Hameury, J. M., Cavecchi, Y., Vanmunster, T., Tordai, T., and Romanov, F. D.

Subjects
MASS transfer, X-ray binaries, ACCRETION disks, WHITE dwarf stars, CATACLYSMIC variable stars, LIGHT curves
Abstract

ASASSN-21au is an ultracompact accreting white dwarf binary (AM CVn type) with a period of ∼58 minutes. Using multiwavelength observations of the system, we discovered a dichotomy in the behavior of outbursts in AM CVns. The binary showed an initial increase in brightness that lasted for at least 82 days, followed by an additional increase that lasted two weeks. Afterward, ASASSN-21au went into superoutburst with a total duration of 19 days, showing an amplitude with respect to quiescence of ∼7.5 mag in g, with a precursor and an echo outburst. A correlation between X-rays, UV, and optical was identified for the first time in an AM CVn during this stage. The color evolution of ASASSN-21au indicates that during the superoutburst the dominant component was the accretion disk. The short duration, large amplitude, and color evolution of the superoutburst agree with expectations from the disk instability model. These characteristics are opposite to those observed in SDSS J080710+485259 and SDSS J113732+405458, which have periods of ∼53 minutes and ∼60 minutes, respectively. The initially slow increase in brightness in the light curve of ASASSN-21au and the behavior after the superoutburst favor a scenario in which changes in the mass-transfer rate led to disk instabilities, while the outburst mechanism of SDSS J080710+485259 and SDSS J113732+405458 has been attributed to enhanced mass transfer alone. Further observations are needed to understand the origin of this dichotomy. [ABSTRACT FROM AUTHOR]

Published
2022
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5. Possible dwarf nova on the Digitized Sky Survey plates

Author

Romanov, F. D.

Subjects
Astrophysics - Solar and Stellar Astrophysics, FOS: Physical sciences, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

I report the discovery of a new bright variable star in the constellation Scorpius. It is most likely star OGLE BUL-SC23 396060 with position (J2000.0): RA 17:57:59.75, DEC -31:38:07.4. Magnitude range is 14.4 (B) - 21.7 (V). It is visible in the possible outburst on two digitized Palomar Sky Survey photographic plates, which were made 60 years ago. This object was registered as a variable star in the AAVSO VSX under the name of Romanov V1 and with UG: variability type., 6 pages, 4 figures, 2 tables. Published in OEJV #190

Published
2018

6. Space suits

Author

Romanov, F

Subjects
Masers
Abstract

Space suit - life support system

Published
1964

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