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RS OPH Recurrent Nova Observation Report, 2021
Summary: RS OPH is one of only 10 known stars in our galaxy that are recurrent novae.
It is located 4,566 light-years away and is composed of a white dwarf and a red giant.
The dwarf attracts matter from the giant, filling its accretion disk to saturation. As pressure and heat increase, a thermonuclear explosion occurs, and the cycle begins again, lasting approximately 15-20 years.
At its core, RS OPH is a cataclysmic star, therefore a binary star:
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Many binary systems involve a giant star and a white dwarf, so stellar bursts result from the accretion of matter from the latter to the former. © Pearson Ed It is well known, as it is one of the most closely monitored recurring novae. Spectacular, it transitions from a magnitude of 12 to 5 and above. It has been known to have several explosions, including in 1898, 1933, 1958, 1967, 2006, and now 2021. "The first known maximum of RS Oph was only discovered in the early 1900s. An investigation of photographs at the Henry Draper Memorial by Williamina Fleming revealed a spectrum that closely resembled that of Nova Sagittarii and Nova Geminorum (displaying hydrogen lines of H-zeta, H-epsilon, H-delta, H-gamma, H-beta, and also two lines that correspond to the bright bands at 4656Å and 4691Å, in gamma velorum)." When the 1905 circular was published, Edward Pickering confirmed that the star, based on its spectrum and light curves, should be "considered a nova, rather than a variable star, and its proper designation shall be Nova Ophiuchi, No. 3." A study of the light curve by Annie Jump Cannon revealed that the "nova" had experienced a significant increase in luminous intensity in 1898, during which it most likely reached a maximum of about magnitude 5. (https://www.aavso.org/vsots_rsoph)  |
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Light curve of the 2006 explosion. (2006/01/13 to 2006/07/13) It was estimated that it took 167 days to descend before falling back to the star's normal magnitude, i.e., magnitude 12 in V filter.
Light curve of the 2021 explosion. (July 25, 2021 to October 13, 2021), i.e., 66 days later.
(If the curve is similar to that of 2006, a return to normal of 12 is estimated around January 22, 2022.)
2021
In 2021, Irish amateur astronomer Keith Geary was the first to report the surprise explosion of RS Ophiuchi, one of the few known recurring novae. He photographed it with a magnitude of 5.0 using his DSLR camera at 22:20 UT on August 8 and confirmed his observation with binoculars. Another AAVSO member, Alexandre Amorim from Brazil, also spotted the eruption 25 minutes earlier. I also have the honor of being the first to provide a spectrum of the star to the scientific and PRO/AM community.
Surprisingly, RS Ophiuchi explosions behave very similarly to one another. Typical explosions show a rapid increase in brightness from quiescence to around magnitude 5 over a 24-hour period. The decline occurs in three distinct stages: the first stage (t1) is rapid, the second (t2) slower, and the third (t3) is intermediate, as shown in the table below.
The variable star then generally returns to its minimum magnitude within about 100 days after the explosion, after which there is a slight brightening to magnitude 9 approximately 700 days after the start of the explosion. In contrast, the intervals between explosions tend to differ from one another, with no common period detected. At its minimum, the light curve shows irregular brightness variations between 1 and 3 magnitudes. Fascinatingly, at the time of writing (63 days after the explosion), the star remains stable at magnitude 10 in V. We await what comes next!
The equipment and methods of observation and processing
Observations were made at the OMSJ using its two parallel telescopes:
Photometry:
ED127 apochromatic triplet refractor with a focal length of 927 mm and an ST-7 XME camera equipped with Johnson/Cousin B, V, R, and I photometric filters. The field of view (FOV) is 9 x 16.6 arcminutes and the pixel scale is 1.95 arcseconds/pixel.
Spectroscopy:
Celestron C14 telescope equipped with a 0.63 focal reducer to obtain a focal length of 2463.3 mm and an Alpy-600 spectroscope equipped with the Titan-Atik guiding module and an Atik 414ex camera.
All images were calibrated using bias and dark frames calibrated at -20 degrees Celsius, and the photometric analysis processes were performed using MaximDL software. The same was done for the spectroscopic images, except that they were processed with BassProject software.
The results are available at AAVSO and on the ARAS website.
*TEMPERATURE CALCULATED BY B-V:
It is important to note that we have intentionally omitted the star's temperature based on B-V at different stages of nova development. RS OPH is a symbiotic nova, composed of a white dwarf and a red giant, which completely distinguishes it from classic or dwarf novae. Furthermore, symbiotic stars tend to shed a lot of material around them, making it difficult, if not impossible, to read the star's surface. This is therefore a dynamic system with too many elements that can interfere with accurate calculations. Using B-V or other filter colors when dealing with such a complex dynamic system is a mistake, especially since the link between the effective surface temperature and everything related to the spectral distribution requires the object to radiate as a black body or be at least static. However, with RS OPH, this is neither the case.
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References: AAVSO reference chart with comparison table: http://aavso.org/vsp Requested scale: "E (30 arcmin)"
Variable Star Plotter Field photometry for RS OPH from the AAVSO Variable Star Database Data includes all comparison stars within 0.25° of Report this sequence as X26796EZ in the chart field of your observation report.
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Observations:
First observation, during the night of August 8-9, 2021:
Moderately difficult conditions: Cloud cover of 0 to 25%, temperature inside the dome ranging from 18.1 to 22.9 degrees Celsius, and an average relative humidity of 80%.
SQM reading for the night:
Photometric reading
Spectroscopy: This first basic spectrum taken on 2021/08/9.1235, raw and without continuum curve corrections,
would be the first spectrum declared to the amateur and scientific community.
- From a photometric standpoint, because the star eclipsed all the reference stars, the B-band reading was inaccurate, and therefore no B-V reading was obtained at this stage. Even after searching the AAVSO data, we found no B-band filter data.
2021-08-10
Photometry
An apparent B-V of -0.281090909.
2021-08-13
Photometry
An apparent B-V of 0.6504.
2021-08-26
Photometry
An apparent B-V of 0.7618333.
2021-08-30
Photometry
No B-V.
2021-09-10
Photometry
An apparent B-V of 0.717333337.
2021-09-16
Photometry
An apparent B-V of 1.03314286.
Spectroscopy
Observation using low-resolution spectroscopy:
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2021-08-08-10 |
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2021-08-08-13 |
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2021-08-08-26 |
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2021-08-08-30 |
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Compilation:
Conclusion:
According to the document "arXiv:2109.01101v1 (astro-ph.sr) 2 Sept 2021", the mass of the RS OPH dwarf is calculated to be 1.33 solar masses (MS).
An older document, "The Astrophysical Journal, 558:323-350, September 1, 2001", also calculated the mass of the RS OPH dwarf, indicating a mass of around 1.377 MS. Despite these variations between calculations, this still places the star very close to the Chandrasekhar critical mass, implying that the star is a candidate to become a Type Ia supernova.
An interesting point in the ongoing cycle of this recurrent symbiotic nova is that, during its quiescence period, a slight variability in the B band is observed. This occurs through the exchange of material from the donor to the accretion disk; the junction point is the "hotspot" and shines in this temperature band. Shortly after its explosion in August 2021, this variation had, of course, disappeared, given that the accretion disk had been destroyed. However, a document titled "Flickering Returns as RS Oph Reestablishes Quiescent Conditions Following its 2021 Nova Outburst" (https://ui.adsabs.harvard.edu/abs/2022RNAAS...6..103M/abstract) informs us that on March 9, 2022, 212 days after the eruption, RS Oph still showed no detectable flicker.
The reappearance of twinkling coincides with the rise in the B-band light curve around March 22, 2022 (+225 days).
From day +250 onward, the recorded twinkling amplitude appears to depend more on the actual observation date than on the B-band brightness of RS Oph.
By day +260, RS Oph had regained the same B-band brightness that characterized the first 10 years of quiescence following the 2006 explosion, indicating that the immediate circumstellar space in RS Oph has refilled the accretion disk, which has returned to its pre-explosion conditions.
It also mentions the following regarding the mass of the accretion disk:
"Such a disk is probably less massive and extensive than it was during the five years preceding the 2021 eruption, when the quiescence luminosity of RS Oph increased by ∆B=0.3 mag. This suggests that, similarly to what is observed in T CrB (Munari et al. 2016; Luna et al. 2020), also in RS Oph, accretion on the WD is not regular and constant between explosions, but is instead of a more episodic nature."
Another paper (https://iopscience.iop.org/article/10.3847/2515-5172/ac6de9) describes a new method for determining when a nova, such as RS OPH, returns to "normal."
This method is based on the reionization of ejecta by photoionization using radiation released into the boundary layer by accretion.
To learn more... Another link: the variability of RS OPH in the B band (The recurrent nova RS Oph - simultaneous B and V band observations of the flickering variability)
I'll let you read it...
Acknowledgments:
I would like to warmly thank my friend Malhar Kendurkar, who has taught me so much and from whom I continue to learn. Steve Shore from the University of Pisa, whose lectures and guidance have helped to demystify these "recurrent" novae, making them easier to understand. We cannot overlook the involvement of the AAVSO, which has provided the graphs and references and has been training amateur astronomers in the science since 1911.
The next one to watch is T CRB, which is due soon (2025-2026)?
Référence sur le net:
https://apod.nasa.gov/apod/ap210822.html
https://www.aavso.org/vsots_rsoph
https://skyandtelescope.org/astronomy-news/recurrent-nova-rs-ophiuchi-just-blew-its-top/
https://fr.wikipedia.org/wiki/RS_Ophiuchi
https://trustmyscience.com/nova-etoile-rare-brillante-possible-observer-oeil-nu/
https://aras-database.github.io/database/rsoph.html
https://www.astrogeo.va.it/ans_spectroscopy/sup/20220119_index.html
https://ui.adsabs.harvard.edu/abs/2022RNAAS...6..103M/abstract
https://iopscience.iop.org/article/10.3847/2515-5172/ac6de9
https://articles.adsabs.harvard.edu/pdf/2012BASI...40..185S
https://iopscience.iop.org/article/10.3847/2515-5172/ac6de9
https://arxiv.org/abs/1807.01555
Monographie AAVSO #7 : RS Ophiuchi 1890 - 1995
Bode, MF, éd. RS Ophiuchi et le phénomène Nova récurrent . Utrecht : VNU Science P, 1987. ISBN 90-6764-074-3
Hack, M. et C. la Dous, éd. Variables cataclysmiques et objets associés . Washington, DC : Direction de l'information scientifique et technique de la NASA, 1993.
Livio, Mario, James W. Truran et Ronald F. Webbink. " Un modèle pour les explosions du récurrent Nova RS Ophiuchi ." The Astrophysical Journal , 308, 1986, 736-742.
Mauche, Christopher W. a un site Web merveilleux et informatif dans lequel il donne un excellent examen des variables cataclysmiques.
Oppenheimer, Benjamin D. et Janet A. Mattei. " Analyse des observations AAVSO à long terme de RS Ophiuchi. " Journ. AAVSO , 22, 1993, 105-109.
Sekiguchi, K. " Novae récurrentes. " Astrophysique et sciences spatiales , 230, 1995, 75-82.
Snijders, MAJ " Observations multi-fréquences de l'explosion de 1985 de RS Ophiuchi ." Astrophysique et sciences spatiales , 130, 1987, 143-254.
Warner, Brian. Étoiles variables cataclysmiques . New York : Cambridge UP, 1995. ISBN 0-521-41231-5.
Webbink, Ronald F., Mario Livio, James W. Truran et Marina Orio. " La nature des novae récurrentes ." The Astrophysical Journal , 314, 1987, 653-672.
Webbink, RF, M. Livio, JW Truran et M. Orio. " La nature des novae récurrentes ." Astrophysique et sciences spatiales , 131, 1987, 493-495.
JBD 2022 - Révision 2025